Improved methods for the synthesis of 8-hydroxyacyclovir and 9-(carboxymethoxymethyl)guanine, metabolites of acyclovir, were examined. The methods were found to be useful for practical preparation of 8-hydoxyacyclovir and9-(caboxymethoxymethyl)guanine of high purity. Careful spectroscopic analysis of 8-hydroxyacyclovir in DMSO-d 6 suggested that it may be exist in an 8-oxo tautomer rather than an 8-hydroxy